ASoC: sigmadsp: Fix missleading return value

Forwarding the return value of i2c_master_send, leads to errors
later on, since i2c_master_send returns the number of bytes
transmittet. Check for ret < 0 instead and return 0 otherwise.

Signed-off-by: Pascal Huerst <pascal.huerst@gmail.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>